1. Field of the Invention
The present invention relates to an occupant restraint device which includes a deployable air bag disposed in a folded-up state along an upper edge of a door opening in a vehicle body. The air bag is expanded by a high-pressure gas generated by an inflater in a curtain-shape along an inner surface of a side of a vehicle compartment upon collision with a vehicle.
2. Description of the Related Art
Such an occupant restraint device is known, for example, from Japanese Patent Application Laid-open No.10-278723.
The occupant restraint device described in the above Publication includes an inflater disposed at a lower portion of a front pillar and an attached air bag. A high-pressure gas generated by the inflater is supplied to a front end of the air bag, disposed along an upper edge of a door opening in a vehicle body, to deploy the air bag in a curtain-shape into a vehicle compartment.
In general, the air bag of the occupant restraint device is comprised of a congregation of a large number of expandable cells and folded into an longitudinally elongated shape to extend from a front pillar past a center pillar to a rear pillar of the vehicle. When the high-pressure gas is supplied from the inflater to one end of such longitudinally elongated air bag, a time lag exists between the expansion of the first end of the air bag and the expansion of the opposite rear end. For this reason, the expansion of the rear end is retarded, resulting in a possibility of underperformance of the occupant restraint device. If the volume of the gas propelled by the inflater is increased in order to solve such problem, it is a possibility that the internal pressure in the cell or cells approximate the inflater is increased excessively, and as a result, such cell can be damaged. In addition, when a portion of the air bag is damaged, the high-pressure gas can still be supplied to a cell group extending from the inflater to short of the damaged portion to expand the cells of such group. However there is a difficulty in supplying high-pressure gas to a cell group located beyond of the damaged portion, thus incompletely expanding the cells of such cell group, resulting in reduced performance.
The occupant restraint device described in the above Patent is designed to commonly fasten the folded air bag and an air bag holder to the vehicle body by a common bolt. The air bag is disposed within an air bag case made of a synthetic resin. The bolt is passed through a mounting portion, extending in a flange-shape, of the air bag case, the base end of the air bag and the air bag holder to fasten them to the vehicle body.
In the known occupant restraint device, in order to reliably support the folded air bag on the air bag holder, it is necessary to accommodate the air bag within an air bag cover formed of a synthetic resin and having a high rigidity. When a simple air bag cover such as a fabric is used, it is difficult to correctly position the air bag in the air bag holder. An air bag cover having a high rigidity is requisite. However this is disadvantageous with respect to the weight and the cost.
The front end of the air bag of the occupant restraint device described in the above Patent is disposed in a folded state in a space sandwiched between the front pillar and the front pillar garnish. The air bag, when expanded upon collision of the vehicle, enters a passage defined between the front pillar and a large number of rib-shaped energy absorbing members provided on an inner surface of the front pillar garnish. The expanding air bag forces the front pillar garnish open and the air bag fully deploys through the resulting opening into the vehicle compartment.
In the above known occupant restraint device, however, a pointed or sharp corner or edge exists on the surface of each of the energy absorbing members facing the passage. For this reason, when the air bag is expanded to force the front pillar garnish open, there is a possibility that the air bag will be caught on the sharp comers of the energy absorbing members, whereby the smooth and even deployment of the air bag will be impeded damaging the air bag.
In addition, the occupant restraint device described in the above Patent includes the inflater disposed at the lower portion of the front pillar, so that the high-pressure gas generated by the inflater is supplied to the front end of the air bag disposed along the upper edge of the door opening in the vehicle body, to deploy the air bag in the curtain-shape into the vehicle compartment.
The above description for Japanese Patent Application Laid-Open No. 10-278723 applies generally to the known prior art.
In order to solve such problem, it is conceived that a plurality of cell groups, with their internal spaces independent from one another, are defined in the air bag, and the high-pressure gas is supplied to a high-pressure gas supply port provided in each of the cell groups. However, if additional inflaters are mounted in correspondence to the separate cell groups, the number of the inflaters is increased, increasing the cost and the weight of the device.
The air bag of the inflatable curtain device described in the above Patent Application Laid-open No. 10-278723 includes the plurality of cells disposed in the longitudinal direction of the vehicle body, wherein the diameter of the cells in front and rear of the center pillar is larger than those of the other cells. Therefore, when a head of an occupant sitting on a front seat urges against the air bag toward the vehicle body, the larger-diameter cells are caught on a rear surface of the center pillar, whereby the forward movement of such cells is hindered. Thus, the tension of that portion of the air bag located ahead of the center pillar is maintained, leading to an enhanced performance of holding back the occupant sitting on the front seat.
The occupant restraint performance required for an air bag of an inflatable curtain is the highest at a location approximate to a pillar having a high rigidity and relatively low at a location approximate to a door glass. For this reason, it is necessary to promptly expand those cells of the air bag which are located in the vicinity of the pillar. In the above known occupant restraint device, however, the diameter (and volume) of the cells located immediately in the rear of the pillar is larger, and for this reason, there is a possibility that the expansion of the larger-diameter cells takes more time than expansion of the other cells, resulting in a reduced occupant restraint performance.
Such occupant holding-back device is known, for example, from Japanese Patent Application Laid-open No.9-254734.
The occupant restraint device described in the above Patent is designed, so that an air bag is disposed in a vertically zigzag folded state within a cover and is expanded by a high-pressure gas supplied from an inflater to force a cut portion of a lower surface of the cover open to become deployed downwards into a vehicle compartment upon collision with another vehicle.
FIGS. 26A to 26D show the course of deployment of the air bag of the above known occupant restraint device, wherein an upper base end of the air bag shown in section indicated by an open circle, and a lower tip end of the air bag is indicated by a black dot.
The nonexpanded air bag is folded in the vertically zigzag manner (see FIG. 26A). When the high-pressure gas is supplied from the inflater to the base end of the air bag, due to collision of the vehicle, the expansion of the air bag is started at its base end (see FIG. 26B). In the course of spreading of the expanded area of the air bag from the base end toward the tip end thereof, the tip end may be caught on the inner surface of the side of the vehicle compartment (on an inner surface of the pillar or a door) in some cases (see FIG. 26C). When the high-pressure gas is further supplied in this state to start the expansion of the air bag at its tip end, the rigidity of the air bag is increased by an increase in internal pressure, because the air bag is intended to extend straight. As a result, the tip end of the air bag may be strongly urged against the inner surface of the side of the vehicle compartment and the air bag maybe bent into a at an intermediate portion thereof and fail to be deployed smoothly and evenly downwards (see FIG. 26D).